In order for integrated circuit (IC) processing to be cost effective, the individual circuits, or devices, are typically mass produced using a semiconductor wafer to make many devices on a single substrate simultaneously. A typical process flow for integrated circuits follows the steps of device fabrication, device testing, device separation, and device packaging. When the devices are separated from a wafer, dicing debris, comprised of wafer particles and dust, is created. This dicing debris is washed from the surface of the IC prior to bonding the device to the package.
Microelectronic mechanical systems (MEMS), or micromechanical devices, often have structures that are too fragile to survive exposure to some of the standard IC fabrication steps such as device separation and cleanup. The fragile nature of some MEMS, for example the digital micromirror device (DMD) and some accelerometers, requires that the standard IC process steps be reordered to avoid damaging the completed devices. DMDs are explained in U.S. Pat. No. 5,061,049, "Spatial Light Modulator and Method", which is assigned to Texas Instruments Incorporated. Accelerometers are described in U.S. Pat. Ser. No. 08/142,548, "Digital Accelerometer", which is also assigned to Texas Instruments Incorporated. As described in the aforementioned patents, these MEMS have very small structures suspended over an air gap above electrodes formed on the surface of a silicon substrate. Once these structures are formed and the sacrificial material is etched from the air gap, the devices are very fragile. The devices cannot be exposed to liquids, such as would occur during water cleanup steps, without risking destruction of the mirror. Therefore, the devices must be cut and the dicing debris washed away before etching the sacrificial material from underneath the mirror.
Wafer separation prior to device completion results in extensive device handling during the remaining device fabrication steps such as passivation and device testing. Performing these processes in wafer form as opposed to device form greatly reduces the necessary handling because the processing equipment must only move and align to one wafer instead of many devices. Precise alignment is very critical for die testing.
This invention discloses a method wherein the entire device fabrication and testing process can be completed using wafer processing techniques.